A typical manufacturing process for a component of, e.g. a gas turbine engine, involves producing a forging, heat-treating the forging, and then machining the forging to produce the final component. The forging is thus a supplied part that envelopes the material of the final component.
Components formed in this way can be high value and safety critical, such as rotor discs. They are commonly ultrasonically inspected to detect anomalies that may be introduced by melting, forging and heat treatment processes before final machining. If an anomaly is detected, the component may be scrapped.
If a component is to be scrapped, it is preferable from a cost point of view that the anomaly is detected as early in the manufacturing process as possible. Accordingly, ultrasonic inspection is often performed on the supplied part, e.g. the heat-treated forging envelope, rather than on the final machined component. Also, the surface geometry of the supplied part is generally simpler than that of the final component, making ultrasonic inspection of the supplied part correspondingly simpler.